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The aim of the study was to understand the releasing characteristics of sediment phosphorus (P) in all fractions under varying environmental conditions and the relationship between sediment P and eutrophication in shallow city lake, Donghu Lake of Wuhan in China. Effects of P concentration in overlying water, oxygen, light, pH, temperature, and agitation intensity on release processes of sediment P in all fractions in Donghu Lake, China, were investigated. The release quantity and release rate of sediment P in the distilled water were significantly higher than those of lake water, and under anaerobic condition, they were higher than those of aerobic treatment. The concentrations of each P form decreased obviously in both dark and irradiated systems. Both high and low pH promoted the release of Fe/Al-P, IP, and TP, but Ca-P decreased sharply with decreasing pH, while the difference of OP was not obvious. The release rate of each P form accelerated drastically when water temperature rose from 5 to 30°C. The magnitude of the each P form released increased with the increase in the agitation intensity at the first 6 d, while it showed no significant difference after 8 d in different agitation intensities (100–200 rpm). The results showed that the extent of P in all fractions released from Donghu Lake sediment was affected variously by the environmental factors, and the sediment was unstable, at risk of releasing P to Donghu Lake. [ABSTRACT FROM AUTHOR]

The removal efficiency of sediment phosphorus (P) in all fractions with a combined technology of porous ceramic filter media (PCFM) and submerged macrophytes was studied in Donghu Lake, Wuhan, China. The adsorption kinetic models of the sediment P in all fractions on PCFM could be described well by a power function equations (Q t = k · t a , 0 < a < 1). The P removal capacity of the combination of PCFM and Potamogeton crispus, a submerged macrophyte, was higher for all P forms than that of the combination of PCFM and another macrophyte, Vallisneria spiralis . This study suggested that the combination of PCFM and macrophytes could achieve a synergetic sediment P removal because the removal rates of the combinations were higher than the sum of that of PCFM and macrophytes used separately. The combined technology could be further applied to treat internal P loading in eutrophic waters. [ABSTRACT FROM AUTHOR]

• The biomass of phytoplankton was highest in summer and lowest in winter. • Water quality, followed by land use, had the strongest influences on phytoplankton. • Land use and lake morphology affecting phytoplankton biomass were indirect. • Lake area was negatively correlated with phytoplankton biomass. The community composition and biomass of phytoplankton in shallow lakes are impacted by many environmental factors including water quality physicochemical parameters, land use in the watershed, and lake morphology. However, few studies have simultaneously evaluated the relative importance of these factors on the effect of community composition and biomass of phytoplankton. The relative importance of the water quality physicochemical parameters (water temperature [WT], total nitrogen [TN], total phosphorus [TP], pH, dissolved oxygen [DO], electrical conductivity [EC], turbidity and Secchi depth [SD]), land use (built-up land, farmland, waters, forest, grassland, and unused land) in the watershed, and lake morphology (area and depth) on the composition and biomass of phytoplankton communities were assessed in 29 subtropical shallow lakes in Wuhan, China, during different seasons from December 2017 to November 2018. The results showed that phytoplankton in all 29 lakes was mainly composed of Cyanophyta, Chlorophyta, and Bacillariophyta. Phytoplankton abundance was highest in summer and lowest in winter. We analyzed the relative importance of the three groups of variables to the community composition of the phytoplankton by variance decomposition. The results showed that the three groups of environmental variables had the highest explanation rate (> 80%) for the composition of the phytoplankton community in summer and autumn, and the explanation rates in spring and winter were 42.1% and 39.8%, respectively. The water quality physicochemical parameters were the most important variables affecting the composition of phytoplankton communities, followed by land use in the watershed. Through generalized additive model and structural equation model analysis, we found that the land use and lake morphology had minimal direct impact on the Chl-a and cell density of phytoplankton, mainly by altering the TN, TP, turbidity, SD, DO, and EC, which indirectly affected phytoplankton. WT and nutrients were still the main predictors of phytoplankton abundance. Built-up land was the main source of nitrogen and phosphorus in lakes. Correlation analysis found that forest and grassland had positive impacts on reducing lake nitrogen and phosphorus contents. This showed that increasing grassland and forest in the watershed could reduce the pollutants entering the lake. Our findings will contribute to water quality management and pollution control for subtropical shallow lakes. [Display omitted] [ABSTRACT FROM AUTHOR]